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M Vi


If one of the nuclei of hydrazobenzene is already substituted
in the/rtnz-position, the reaction may give rise todiphenylamine
derivatives, which are known as ortho- or para-semidines
>NII-:    x_/
^                         NIL
^>—NH—/     NNIL     x/     X)-NII-<^     N
j                                                   Para-semidine.                                             Orlho-semidme.
|,                          Benzidine and its homologues are used in the manufacture of
11..                    valuable azo-colours, congo-red^ bcnsopurpurin, &c. (seep. 291).
<V '                                                   PREPARATION 52.
\^                       Phenylhydroxylamine.—The   necessity for   conducting
{,,   |                      the   reduction   of nitrobenzene   in   neutral   solution  has  been
,Lj 5                        explained in the  previous note.    In  addition   to  the  reagent
'j'i                          named in the preparation,  the aluminium-mercury couple   in
^ ff                      presence of water or ammonium sulphide in alcoholic solution
^?|                      may   be   also   used.    The   conversion   of   nitrobenzene   into
;S*f                      ^-aminophenol  on  electrolysis   in  acid  solution  will  also   be
evident from the fact that phenylhydroxylamine readily under-
goes isomeric change. Phenylhydroxylamine reacts with
nitrous acid, forming a nitroso-derivative,
CflH3NHOH + UNO., = CBH0N(NO)OH -f-II,O.
It also condenses with aldehydes irf the following way :
Nitrosobenzene, which shares the general character of nitroso-
compounds in giving rise to a green vapour or solution, is
readily reduced to phenylhydroxylamine and aniline. It
condenses with ammo-compounds, yielding azo- or diazo-
C6H,NO + H2N.C(5H, = CBH5N = N.C,irfi -I- IIaO.
C6H5NO + H2N.OIi   = C61I0N = N.OH + H2O.